 Defect skipping was introduced in 1974 with the 3340 attached via the 3830 Model 2 Storage Control Unit or integrated attachments on small systems.Defect skipping was essentially a factory only feature until 1981 when CCWs for management along with associated utilities were released.First introduced with the 3380 DASD on the 3880 Storage Control Unit in 1981 the feature was included with the later CKD DASD subsystems.